et al.

RESEARCH ARTICLES
782
similar to reduced organic macromolecular carbon
that has been identified in several shergottites
and a single nakhlite meteorite (fig. S15) (30),
indicating that the production of organic carbon
from abiogenic processes in the martian interior
may not be unique to SNC-like source regions in
Mars. Steele et al.(31) also demonstrated that the
formation mechanism of MMC requires reducing
magmatic conditions consistent with oxygen fugacities
below the fayalite-magnetite-quartz (FMQ)
buffer. Consequently, much of the ferric iron in the
oxides of NWA 7034, as evidenced by electron
probe microanalysis and XRD, was likely a product
of oxidation subsequent to igneous activity as a
result of secondary processes.
Bulk carbon and carbon isotopic measurements
on NWA 7034 were also carried out at
Carnegie, using combustion in an elemental analyzer
(Carlo Erba NC 2500) interfaced through a
Conflo III to a Delta V Plus isotope ratio mass
spectrometer (ThermoFisher) in the same manner
as the data reported by (31, 32) [see(8)]. These
data indicate that carbon is present within mineral
inclusions in NWA 7034 at concentrations of at
least 22 T 10 ppm, and that the d 13 C isotopic value
of this carbon is –23.4 T 0.73‰, which is very
similar to previous bulk C and d 13 Canalysesof
carbon included in shergottite meteorites analyzed
in the same manner (31, 32). These data
indicate that multiple geochemical reservoirs in
the martian interior may have similarly light d 13 C
values. The bulk C concentration in the untreated
sample performed in these measurements was
2080 T 80 ppm C, with a corresponding d 13 C
value of –3.0 T 0.16‰. Scattered carbonate veinlets
from desert weathering were observed by
backscatter electron imaging and element mapping
with the electron microprobe, especially
in the near-surface material but less frequently in
the deeper interior slices of NWA 7034. Although
this carbonate is below the detection limits of our
XRD analyses of the bulk sample and is thus a
minor phase within the meteorite, we believe that
this weathering product is sampled in our bulk
carbon and carbonate analyses (8) (fig. S16).
Oxygen isotopes. Measurements of oxygen
isotopic composition were performed by laser
fluorination at UNM on acid-washed and non–
acid-washed bulk sample and at the University of
California, San Diego (UCSD), on vacuum preheated
(1000°C) bulk sample (table S4). The
triple oxygen isotope precision on San Carlos
olivine standard [d 18 O=5.2‰ versus standard
mean ocean water (SMOW); D 17 O=0‰] analyzed
during sessions at UNM was D 17 O=T0.03‰;the
precision at UCSD using NBS-28 quartz standard
(d 18 O = 9.62‰) was also D 17 O=T0.03‰. In
total, we carried out 21 analyses of bulk NWA
7034 (Fig. 6). The mean value obtained at UNM
was D 17 O=0.58T 0.05‰ (n = 13) for acidwashed
samples and D 17 O = 0.60 T 0.02‰ (n =6)
for non–acid-washed samples; at UCSD the
mean value was D 17 O = 0.50 T 0.03‰ (n =2)
for vacuum preheated samples that were dewatered
and decarbonated. The combined data give
D 17 O = 0.58 T 0.05‰ (n = 21). These interlab
values of bulk samples are in good agreement but
are significantly higher than literature values for
SNC meteorites (D 17 O range 0.15 to 0.45‰)
(33–36). Figure 6 shows that the d 18 O values (5.5
to 7.0‰ versusSMOW)ofNWA7034arehigher
than any determination from the SNC group.
The D 17 O values of the non–acid-washed samples
measured at UNM are similar to and within
Mn (afu)
0.040
0.035
0.030
0.025
0.020
0.015
0.010
0.005
Earth
NWA 7034
error of the acid-washed samples; this indicates
that NWA 7034 has, at most, only minor terrestrial
weathering products, which would drive
the non–acid-washed values closer to D 17 O=
0.00. The slope of the best-fit line to the combined
UNM acid-washed and non–acid-washed data is
0.517 T 0.025, which suggests that the oxygen
isotopic composition of NWA 7034 is the result
of mass-dependent fractionation processes.
Mars
Moon
NWA 7034 Pyroxenes
0.000
0.0 0.2 0.4 0.6 0.8
Fe (afu)
1.0 1.2 1.4
Fig. 2. Fe versus Mn (atomic formula units) showing the trend for all NWA 7034 pyroxenes (cyan dots,
349 microprobe analyses) and, for comparison, pyroxene trends from Mars (red), the Moon (green), and
Earth (blue) (10).
Na 2O+K 2O wt%
10
9
8
7
6
5
4
3
2
1
0
Foidite
Picrobasalt
Tephrite
Trachybasalt
GRS
SNC Meteorites
Basaltic
trachyandesite
Basaltic
Andesite
Trachyandesite
Trachyte
Andesite Dacite
Rhyolite
35 40 45 50 55
SiO2 wt%
60 65 70 75
Fig. 3. Volcanic rock classification scheme based on the abundance of alkali elements and SiO2,modified
after McSween et al.(4). Red dots denote analyses of rocks and soils at Gusev Crater by the Alpha Particle
X-ray Spectrometer (APXS) onboard the Spirit rover (5, 6). The yellow rectangle is the average martian
crust as measured by the GRS onboard the Mars Odyssey orbiter (7). The pink field is the known range of
martian meteorite (SNC) compositions. The cyan dot is the mean value of bulk NWA 7034 as determined
by 225 electron microprobe analyses of fine-grained groundmass; error bars denote SD.
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